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Front. Physiol. | doi: 10.3389/fphys.2018.00134

Short-term sustained hypoxia elevates basal and hypoxia-induced ventilation but not the carotid body chemoreceptor activity in rats

 Karine C. Flor1,  Elaine F. Silva1, Miguel F. Menezes1,  Gustavo R. Pedrino2, Eduardo Colombari1 and  Daniel B. Zoccal1*
  • 1Physiology and Pathology, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Brazil
  • 2Physiological Sciences, Universidade Federal de Goiás, Brazil

Exposure to chronic sustained hypoxia (SH), as experienced in high altitudes, elicits an increase in ventilation, named ventilatory acclimatization to hypoxia. We previously showed that rats exposed to short-term (24 h) SH exhibit enhanced abdominal expiratory motor activity at rest, accompanied by augmented baseline sympathetic vasoconstrictor activity. In the present study, we investigated whether the respiratory and sympathetic changes elicited by short-term SH are accompanied by carotid body chemoreceptor sensitization. Juvenile male Holtzman rats (60-80 g) were exposed to SH (10% O2 for 24 h) or normoxia (control) to examine basal and hypoxic-induced ventilatory parameters in unanesthetized conditions, as well as the sensory response of carotid body chemoreceptors in artificially perfused in situ preparations. Under resting conditions (normoxia/normocapnia), SH rats (n=12) exhibited higher baseline respiratory frequency, tidal volume and minute ventilation compared to controls (n=11, P<0.05). SH group also showed greater hypoxia ventilatory response than control group (P<0.05). The in situ preparations of SH rats (n=8) exhibited augmented baseline expiratory and sympathetic activities under normocapnia, with additional bursts in abdominal and thoracic sympathetic nerves during late expiratory phase that were not seen in controls (n=8, P<0.05). Interestingly, basal and potassium cyanide-induced afferent activity of carotid sinus nerve (CSN) was similar between SH and control rats. Our findings indicate that the maintenance of elevated resting ventilation, baseline sympathetic overactivity and enhanced ventilatory responses to hypoxia in rats exposed to 24 h of SH are not dependent on increased basal and sensorial activity of carotid body chemoreceptors.

Keywords: Active expiration, Carotid Body, chemoreceptor, Hypoxic ventilatory response, sympathetic activity, ventilatory acclimatization

Received: 27 Nov 2017; Accepted: 09 Feb 2018.

Edited by:

Silvia Demoulin-Alexikova, Université de Lorraine, France

Reviewed by:

Jorge Gallego, Institut National de la Santé et de la Recherche Médicale (INSERM), France
Stephen M. Johnson, University of Wisconsin-Madison, United States  

Copyright: © 2018 Flor, Silva, Menezes, Pedrino, Colombari and Zoccal. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Daniel B. Zoccal, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Physiology and Pathology, Rua Humaita, 1680, São Paulo, 14801-903, SP, Brazil, zoccal@foar.unesp.br